In the steam circuits of power stations, water is evaporated and fed under high pressure to a turbine, where the steam expands and cools. The high purity of the water or steam in such a circuit is extremely important, since impurities such as NaCl, CaCO3, MgCO3 etc. largely remain behind as deposits when the water is evaporated, thereby causing damage to the evaporator. Other compounds such as silicates, as well as the smallest quantities of the impurities mentioned above, are entrained in the steam phase and can precipitate onto turbine blades when the steam cools, leading to the possibility of corrosion and fouling in the turbine.
It is known that purity measurements are carried out on the water circuits of power stations, for example to measure the cation conductivity of the water, which is a measure of the purity of the water or steam in the water circuit. In this connection the alkalizing medium added to the water circuit in order to neutralize damaging acids is extracted with the aid of a strongly acidic cation exchanger and cations are exchanged. For example the Na+ from NaCl is extracted from the water and H+ is added to the water in its place, resulting in HCl which has three times greater conductivity than NaCl. The conductivity of the water is therefore measured downstream and in some cases also upstream of the cation exchanger, and a conclusion is then reached about the water purity.